How to convert STEP to Open Collada or other importable format
I made good experiences with FreeCAD (0.16) both transforming to allow import into blender from step/iges data as also the other way around: exporting STLs from blender and then get them to be reshaped in FreeCAD and then exported as step or iges.
FreeCAD is fast, acurate, open source and available for windows, linux and macOS

(sometimes there are holes to stitch and most of the times when transform from step or iges into STL there are a few mesh operations and repairs needed, which work very well in FreeCad too.)

FreeCAD also understands, imports and exports DAE.

here's a little walkthrough for Blenders STL -> STEP/ IGES:
http://northernhope.blogspot.de/2013...h-freecad.html

(of course there are minor inadequaticies due to the transformation, but for me at least, these were always tolarable (below 0.1mm)) so at least for prototyping it proves to be suitable in both directions.